The present invention relates to absorption processes using a desiccant brine as a working fluid to capture solar or waste heat using the combination of an air evaporator and an adiabatic flash chamber.
Kasley, U.S. patent Ser. No. 2,005,377, 1935, describes an absorption power plant using an inexpensive open-air evaporator and using tapwater as boiler feedwater. His plant uses the evaporative capacity of air to drive water from brine in an open cycle and thereby benefits from improved cycle efficiency and reduced costs. However, his plant also boils water directly to steam promoting undesirable corrosion and mineral deposits which may offset the great advantage of the open evaporator. Natanson, U.S. patent Ser. No. 377,300, 1885, describes an indirect, flash-boiling process wherein he heats water in tubes and then flashes the water to steam in a chamber located away from the tubes and thereby allows any minerals to deposit in the noncritical chamber and not in the tubes. However, he does not use the evaporative capacity of air to drive water from liquid desiccant brine in an open cycle. The present invention uses a flash chamber in combination with an open evaporator. The advantage of the open evaporator is that it costs less than any other known evaporator. However, since the open evaporator loses water into the atmosphere, the process must use inexpensive water such as tapwater as makeup. Because of its immunity to minerals, the flash chamber allows the use of tapwater and makes the open evaporator feasible to use. Features of the present invention described herein make the inexpensive, open evaporator practicable.
The adiabatic flash chamber used in the present invention is to be distinguished from the chamber used by Albertson, U.S. patent Ser. No. 4,133,183, who shows water sprayed directly on coils within a vacuum chamber to generate steam. Spraying Albertson's coils with the inexpensive tapwater described herein would form mineral deposits. In loose terms, the flash chamber described herein has no heating coils. Instead, water flows through heating coils located elsewhere and does not vaporize until it enters the flash chamber where it then flashes to steam. In this configuration, minerals deposit in the flash chamber away from the heating coils which would otherwise be harmed by mineral deposits.
The present invention also features a steam absorber which uses a special flow configuration to achieve higher process efficiencies. Desiccant flows within the absorber, absorbs steam and releases heat to warm a stream of water which flows counterflow to the desiccant. The flow of desiccant is configured to prevent backmixing; this prevents the entering rich desiccant from being weakened and diluted by the weak desiccant which has already absorbed substantial amounts of steam. Soddy, Great Britain patent Serial No. 13337, 1952, also describes an absorber configured to prevent backmixing of the desiccant. However, Soddy does not show the counterflow arrangement for sensibly heating a stream of water. Instead, he boils water directly to steam, which for the use of tapwater as described herein, would result in the deposition of minerals from the tapwater onto the heat transfer surfaces. The present invention avoids mineral deposition and achieves higher process efficiencies.